1. Field of the Invention
This invention relates to a method of storing and/or transporting wafers and a method of determining the amount of organic materials attached to stored wafers, and more particularly, to a method of storing and/or transporting wafers in case when non-patterned wafers are stored in a container made of polypropyrene or like organic resins and a method of determining the amount of organic materials attached to stored wafers.
2. Description of the Related Art
In the prior art, it has been a practice that semiconductor wafers, i.e., mirror finished wafers obtained by slicing wafers from an ingot and then polishing, grinding and cleaning the sliced wafers, are transported to an integrated circuit manufacturer for carrying out predetermined patterning processes such as photo-lithography, etching and heat treatment and thin film formation, etc.
The semiconductor wafer manufacturer thus has to supply non-patterned wafers to the integrated circuit manufacturer. The non-patterned wafers obtained after the mirror finishing or after eptaxial growth, have to be accommodated in a wafer case for storage or transport.
FIG. 4 shows a wafer case 50 to this end, which is disclosed in Japanese Laid-Open Utility Model Registration No. 1-129836. As shown, the wafer case 50 comprises a wafer basket 53, which has wafer support grooves 55 for supporting a plurarity of wafers 1 in parallel, a wafer case body 50 for accommodating the wafer basket 53, a wafer case cover top 52 for closing a top opening of the wafer case body 50, and a wafer retainer 54 for retaining the wafers 1 supported in the wafer basket 53.
The wafer case 50 is usually made of polypropyrene, polycarbonate or like organic resins, and it is inevitable that organic materials are dispersed (by volatile emission) from the components of a wafer case. The dispersed organic materials may be attached or adsorbed to the wafers in the wafer case to cause various troubles.
The applicant has earlier proposed, in connection with an SOI structure wafer comprising two mirror finished wafers bonded together via an oxide film formed by thermally oxidizing one of the wafers, a method of storing wafers, in which mirror finished and cleaned wafers are stored in a clean atmosphere free from organic materials until the bonding thereof to prevent the organic materials noted above from being attached or adsorbed to the wafer surfaces and forming numerous non-bonding micro points voids thereon (as disclosed in Japanese Laid-Open Patent Publication No. 4-84431).
With a wafer case made of polypropyrene or like organic resins, however, it is impossible to store wafers in a clean atmosphere free from organic materials, and various attempts have been made to solve this problem.